What the exam asks
- Calculate and compare community diversity using Simpson’s diversity index from raw organism counts.
- Identify and explain how interspecific interactions (, , , ) and intraspecific cooperation drive population trajectories over time.
- Predict and justify how adding or removing a predator triggers a trophic cascade or drives niche partitioning.
- Evaluate statistical significance between experimental community samples by inspecting whether error bars overlap.
Core ideas
Community structure and Simpson’s diversity index
A biological community is defined by its species composition (the identity of species present) and species diversity (which combines species richness, the number of different species, and relative abundance, the proportion of each species).
The AP Biology Equations and Formulas sheet gives Simpson’s diversity index as:
- = total number of organisms of a particular species
- = total number of organisms of all species
Values range from to . A value closer to indicates higher diversity (high richness and high evenness). Communities with higher diversity are generally more resilient to environmental disturbances.